What Is a Myelin Sheath?

Medically Reviewed by Melinda Ratini, MS, DO on August 20, 2021
2 min read

Myelin sheaths are sleeves of fatty tissue that protect your nerve cells. These cells are part of your central nervous system, which carries messages back and forth between your brain and the rest of your body.

If you have multiple sclerosis (MS), a disease that causes your immune system to attack your central nervous system, your myelin sheaths can be damaged. That means your nerves won't be able to send and receive messages as they should.

Because of this, MS can weaken your muscles, damage your coordination, and, in the worst cases, paralyze you. MS affects about 1 million Americans, and it usually shows up between ages 20 and 50. It's not clear what causes it, and there's no known cure.

nerve cell illustration

The myelin sheath wraps around the fibers that are the long threadlike part of a nerve cell. The sheath protects these fibers, known as axons, a lot like the insulation around an electrical wire.

When the myelin sheath is healthy, nerve signals are sent and received quickly. But if you have MS, your body's immune system treats myelin as a threat. It attacks both the myelin and the cells that make it.

When that happens, the nerves inside the sheath can be damaged. That leaves scars on your nerves -- known as sclerosis -- and that makes it harder for them to carry the messages that tell your body to move.

A lot of the research into MS is focused on boosting your body's ability to repair damaged myelin. Scientists are looking into:

  • Ways to prevent the chemical reactions that lead to myelin damage
  • Drugs or experimental treatments that might prevent or fix multiple sclerosis
  • Which antibodies -- the disease-fighting proteins your immune system makes when you get sick -- attack myelin
  • If stem cells -- which can grow into different types of tissues -- can be used to reverse the damage caused by MS